1. Field of Invention
The invention relates to an illuminating device and a projector, and more particularly, to a technique for providing an illuminator for use in combination with a liquid crystal type spatial light modulator.
2. Description of Related Art
In related art projectors, the spatial extent in which an effective beam exists in an optical system including a light source and a spatial light modulator can be represented as the product of the area and the solid angle (etendue: geometrical extent). The product of the area and the solid angle can be conserved in the optical system. The angle that allows the spatial light modulator to take in light that can effectively be modulated is limited. Therefore, when the spatial extent of the light source increases, effective use of the beam from the light source is difficult.
A related art illuminating device for a projector including a liquid crystal type spatial light modulator has, for example, a PBS array as a member for polarization conversion. The PBS array divides a beam into two polarized beams that oscillate in approximately orthogonal directions to each other and one of the beams is converted by a phase plate. Therefore, the use of the PBS array approximately doubles the beam. Particularly when light emitting diodes (LEDs) as a solid light emitting device in an array are provided as a light source, the light emitting area of the light source is large. Consequently, the combination of an LED array and a PBS array should cause the beam to be enlarged and the illumination efficiency should be lowered. Therefore, with an array of LEDs, polarized light in a particular oscillation direction must be supplied without increasing the etendue. The technique for supplying polarized light in a particular oscillation direction without increasing the etendue is disclosed, for example, in Japanese Patent Laid-Open No. 2000-221499 and Japanese Patent Laid-Open No. 2003-57445.